WEAKENED PLO SPARKS MIDEAST PEACE HOPES

Optimism is a commodity in short supply in the Middle East, with good reason. So when King Hussein of Jordan told President Reagan last month that the Palestine Liberation Organization finally was ready to accept negotiations with Israel, there was no shortage of skeptics, especially in Israel.

But the Jordanians -- who themselves have no illusions about the reliability of the PLO's wily Yasir Arafat -- believe they have a solid basis for their new optimism, and it is persuasive enough to have infected Secretary of State George Shultz. They think circumstances in the Middle East have shifted in the last few months to create the best chance yet to get the PLO committed to peace talks.

The wooing of Arafat remains critical because some sort of PLO blessing still is necessary before even non-PLO Palestinians will risk joining Jordan to negotiate with Israel. But the Jordanians believe Arafat's current political weakness can be exploited to get the bargaining going.

Last month Hussein announced on the White House lawn that the PLO has accepted U.N. Resolutions 242 and 338 as a basis for a settlement. Those resolutions call for an exchange of Israeli-occupied lands for peace. "This is a historic breakthrough," the king said later in the week. "It is the first time in the 39-year-old history of the conflict that Palestinian leaders and their people have been willing to accept a negotiated settlement of the problem."

The problem, as the skeptics point out, is that Arafat has not said he will accept Resolution 242. But neither has he yet denied Hussein's words.

Getting that endorsement, say the Jordanians, is the aim of a meeting that they hope will take place soon between the United States and a joint Jordanian-Palestinian group. What makes them hopeful that this time they can corral the elusive Arafat is the Shiite Muslim defeat of Arafat's forces in the refugee camps in Beirut.

Despite the PLO's forced exodus from Beirut in 1982 and the defeat and expulsion of Arafat's remaining forces at Tripoli, Lebanon, in 1983, the PLO leader still nursed the hope of re-establishing bases in the camps once the Israelis left Lebanon.

But the Shiites, with Syria in the background, now have made it clear that such hopes are pure fantasy. The death of dreams of re-establishing a military option leaves Arafat with only one arena in which to exercise his dwindling influence, the diplomatic one. The Lebanon defeat will give credence among Palestinians to the argument that Arafat has no choice but to bargain. The role played by Syria in the camp slaughter will undermine his critics in Damascus.

Even more important, the latest PLO disaster in Beirut completes a shift in Arafat's constituency. Before 1982, when the PLO was based in Lebanon, its primary constituency was in the camps there where it had created a state within a state. But those refugees originated from the parts of Palestine that now lie within the pre-1967 borders of Israel.

For refugees in Lebanon, the creation of a mini-state on the West Bank and Gaza Strip, occupied by Israel after 1967, was wholly inadequate. They wanted the destruction of the Israeli state so they could return to their original villages. Their hard-line demands colored the program of the PLO.

With Arafat's forces routed from those ruined camps, the West Bank and Gaza have become the PLO leader's only constituency. "This is a major difference," said one Jordanian official. "Before, Arafat felt committed to the hopes of those in the Lebanese camps. Now his constituency on the West Bank has different hopes. They want to get rid of Israeli occupation by any means, including negotiations."

But to have access to his West Bank constituents, Arafat needs the cooperation of Amman. The Jordanians have played this lever like virtuosos.

In his Tunis headquarters Arafat is isolated and out of touch. So he has been welcomed to Amman and put up for weeks in a posh guesthouse. Most important, he is featured on Jordanian television, which is received in the West Bank, giving him his only avenue of direct access to the group of Palestinians on which his leadership depends.

But what the Jordanians give they can also take away. If Arafat won't recognize 242, "he won't be so welcome in Amman," sources say.

What the Jordanians would like to see as a consequence of a joint U.S.-Palestinian-Jordanian meeting is an Arafat statement that would go something like this: "We are ready to negotiate a peaceful settlement with Israel on the basis of Resolutions 242 and 338 provided that we obtain self- determination within the context of confederation with Jordan."

They hope the meeting, and such a statement, would galvanize peace forces within Israel while increasing West Bank pressure on the PLO to pursue talks and undermining anti-Arafat factions.

As for a framework for talks, the Jordanians do not appear wedded to Hussein's proposal for a U.N. Security Council format, involving the Soviet Union and other Arab countries, a format that neither Israel nor the United States wants. They do seek some sort of international umbrella for direct Jordanian-Palestinian-Israeli negotiations.

No one knows better than Hussein how easily such a hopeful prognosis can be derailed. Arafat may not be able to rally sufficient organizational support to pull his PLO wing behind him, or, as many believe likely, he may back out of involvement at the last minute.

But for the time being the Jordanians are playing it one step at a time, hoping each step will nudge the Palestinians and the Israelis closer to dialogue. "The Palestinians need hope, the Israelis need trust," Hussein told an audience during his Washington visit. "It is important for all of us to provide the hope and the trust they need."